Apparatus and method of transcoding video snap image

ABSTRACT

An apparatus and method of transcoding a video snap image is disclosed. The apparatus includes a video decoder for performing a variable length decoding (VLD), inverse discrete cosine transform (IDCT), and inverse quantization with respect to an input bit stream to display the decoded bit stream, a DC extraction section for extracting DC components from discrete cosine transform (DCT) coefficients of variable-length-decoded macro blocks, an adder for averaging the extracted DC components, a differential pulse code modulation (DPCM) section for obtaining and outputting a difference value between the DC component averaged by the adder or the DC component outputted from the DC extraction section and a DC component of a previous macro block, a Huffman encoding section for Huffman-encoding the difference value outputted from the DPCM section, and a storage device for storing a Huffman-encoded snap image and the video bit stream.

This application claims the benefit of the Korean Application No.P2001-36038 filed on Jun. 23, 2001, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a video transcoding apparatus for adigital television (TV) receiver or a digital video appliance, and moreparticularly, to an apparatus and method of transcoding a video snapimage.

2. Discussion of the Related Art

Recently, to reduce the storage and transmission capacity of digitalvideo and audio signals, an MPEG encoder has been used.

Especially, as diverse applications such as a video search,picture-in-picture (PIP), video combining, video editing, conversion oftransmission bit rate, etc., are required with respect to a compressedbit stream, there has been a demand for video transcoding methods thatconvert a specified bit rate of the MPEG bit stream into another bitrate.

For example, such video transcoding methods may convert an MPEG-2 bitstream into a bit stream of H.263, convert a digital video (DV) formatthat is a digital output of a digital camcoder into an MPEG bit stream,or convert a high-definition (HD)-class MPEG bit stream of a highpicture quality into a standard definition (SD)-class MPEG bit stream ofa low picture quality.

Generally, the above-described transcoders adopt encoding methods inwhich an MPEG decoder reduces the bit rate of the bit stream, and thenthe bit stream is encoded to the MPEG bit stream.

However, if it is required to search contents of the MPEG bit streamafter the MPEG bit stream is stored in a storage device such as a harddisc drive (HDD), the search should be performed after the wholecontents of the HD-class MPEG bit stream is decoded, and this causes thesearch to be inconvenient and to take a lot of time.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus andmethod of transcoding a video snap image that substantially obviates oneor more problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide an apparatus and methodof transcoding a video snap image that can easily and rapidly searchcontents of an MPEG stream stored in a storage device.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anapparatus for transcoding a video snap image includes a video decoderfor performing a variable length decoding (VLD), inverse discrete cosinetransform (IDCT), and inverse quantization with respect to an input bitstream to display the decoded bit stream, a DC extraction section forextracting DC components from discrete cosine transform (DCT)coefficients of variable-length-decoded macro blocks, an adder foraveraging the extracted DC components, a differential pulse codemodulation (DPCM) section for obtaining and outputting a differencevalue between the DC component averaged by the adder or the DC componentoutputted from the DC extraction section and a DC component of aprevious macro block, a Huffman encoding section for Huffman-encodingthe difference value outputted from the DPCM section, and a storagedevice for storing a Huffman-encoded snap image and the video bitstream.

Here, the DCT coefficients used for extracting the DC components throughthe DC extraction section is DCT coefficients of an intra (I)-picture,and the DPCM section performs the DPCM in the unit of a slice.

The video bit stream and the snap image bit stream to be stored in thestorage device are connected together to be stored as one signal train,and are discriminated from each other using an unusedextension_start_code_identifier on an MPEG-2 syntax. The bit stream ofthe snap image to be stored in the storage device is composed of animage size, positional information of each slice, data length, and videosnap data in the unit of a Huffman-encoded slice.

Also, the video bit stream to be stored in the storage device iscomposed of a presentation time stamp (PTS) and a video elementarystream (ES).

If a user selects the snap image being displayed, the video decoderdecodes and displays the video bit stream stored in the next position ofthe snap image being displayed, and confirms theextension_start_code_identifier from the input video bit stream. Then,if the identifier is an identifier that is not used on the MPEG syntax,the video decoder skips the video bit stream indicated by the identifierwithout decoding the bit stream.

In another aspect of the present invention, a method of transcoding avideo snap image includes the steps of variable-length-decoding an inputvideo bit stream in the unit of a macro block, extracting DC componentsfrom discrete cosine transform (DCT) coefficients ofvariable-length-decoded macro blocks, obtaining a difference valuebetween the extracted DC component and a DC component of a previousmacro block, and Huffman-encoding the difference value.

Here, the step of obtaining the difference value between the extractedDC component and the DC component of the previous macro block includesthe steps of if the extracted DC component corresponds to a luminance,averaging the extracted DC components of the luminance and thenobtaining the difference value between the averaged DC component of theluminance and the DC component of the luminance of the previous macroblock, and if the extracted DC component corresponds to a color,obtaining the difference value between the extracted DC component of thecolor and the DC component of the color of the previous macro block.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a block diagram of an apparatus for transcoding a video snapimage according to the present invention.

FIG. 2 is a block diagram of a snap image processing section in FIG. 1.

FIG. 3 is a view illustrating an example of a DC extraction process inone macro block of an interlaced scanning sequence performed by a DCextraction section of FIG. 2.

FIG. 4 is a view illustrating an example of a frame structure of anMPEG-2 frame and that of a snap image frame obtained by transcoding theMPEG-2 frame.

FIG. 5 is a view illustrating the structure of a bit stream database tobe stored in a storage device in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention is to rapidly search contents of an image or toeasily search and reproduce the desired video contents when a digitalvideo sequence of a large capacity is searched and reproduced after itis stored.

For this, the present invention proposes a bit stream structure forstorage in that the original video bit stream is converted into a DCimage of a small size for a video snap, and the DC image is compressedand stored, so that the stored contents can be easily searched.

FIG. 1 is a block diagram of an apparatus for transcoding a video snapimage according to the present invention.

The apparatus includes a packetized elementary stream (PES) decoder 101for decoding and separating a video PES into a video elementary stream(ES) and a presentation time stamp (PTS), a variable length decoding(VLD) section 102 for performing a VLD with respect to the video ESoutputted from the PES decoder 101 or the video ES reproduced through astorage device 106, a video decoder 103 for restoring thevariable-length-decoded bit stream to an original image through aninverse discrete cosine transform (IDCT) and inverse quantization, avideo display section 104 for processing the image outputted from thevideo decoder 103 or a snap image to match with a display format anddisplaying the processed image, and a snap image processing section 105for storing the video ES outputted from the PES decoder in the followingstorage device 106, or transcoding the video ES to the snap image andstoring the snap image in the storage device 106.

Here, the PTS is time management information of a reproduced output. Ifthe first portion of an access unit is included in a packet, the PTS isadded to a packet header, while if not, the PTS is not added to thepacket header.

FIG. 2 is a block diagram of a transcoding section 105 a of the snapimage processing section 105 in FIG. 1.

The transcoding section 105 a includes a DC extraction section 201 forextracting DC components from discrete cosine transform (DCT)coefficients of macro blocks outputted from the VLD section 102, anadder 202 for averaging the DC components of the macro blocks (i.e.,four 8×8 macro blocks) if the DC component extracted by the DCextraction section 201 corresponds to a luminance, a differential pulsecode modulation (DPCM) section 203 for obtaining and outputting adifference value between the DC component of the luminance averaged bythe adder 202 or the DC component of a color outputted from the DCextraction section 201 and a previous DC component, and a Huffmanencoding section 204 for Huffman-encoding the difference value outputtedfrom the DPCM section 203.

The reference numeral 105 b denotes a user interface section in the snapimage processing section 105, which interfaces an operation according toa user's input, i.e., a user's selection of storage, reproduction,search, etc., to the transcoding section 105 a.

In the present invention as constructed above, the PES decoder 101separates the input video PES into the video ES, the PTS, etc., byparsing the input video PES, and then outputs the separated video ES andthe PTS to the snap image processing section 105.

The VLD section 102 separates the input video ES into a picture type,color type, DCT coefficients, etc., by variable-length-decoding thevideo ES, and outputs them to the video decoder 103 and the snap imageprocessing section 105 in the unit of a macro block.

At this time, a path of data outputted from the PES decoder 101 ischanged according as the input image is to be displayed, stored in thestorage device 106 such as the HDD, or converted into the snap image andstored in the storage device 106.

Specifically, in FIG. 1, a solid line indicates a path for storing theinput video PES in the storage device 106 in the form of a video ES inthe unit of a picture through the PES decoder 101 and the snap imageprocessing section 105. A dotted line indicates another path for auser's reproduction and viewing of the stored video ES or the snap imagethrough a search device.

For instance, in case that the input image is stored in the storagedevice 106 such as the HDD, the video ES, the PTS, etc., parsed by thePES decoder 101 are outputted to the storage device 106 through the snapimage processing section 105. In case that the input image is changed tothe snap image and then stored in the storage device 106, the macroblocks variable-length-decoded by the VLD section 102 are outputted tothe snap image processing section 105, converted into the snap image,and then outputted to the storage device 106.

Also, in case that the input image is displayed in the display device,the signal variable-length-decoded by the VLD section 102 is outputtedto the video display section 104 through the video decoder 103.

Meanwhile, in case that the input image stored in the storage device isdisplayed, the video ES stored in the storage device 106 is outputted tothe video decoder 102 through the snap image processing section 105, andthe snap image is outputted to the video display section 104 through thesnap image processing section 105.

The video decoder 103 performs the IDCT and the inverse quantization(IQ) with respect to the bit stream outputted from the VLD section 102in the unit of an 8×8 block to match with the typical MPEG-2 videosyntax.

At this time, if the input bit stream corresponds to an intra-picture(I-picture), the result of IQ/IDCT is directly outputted to the videodisplay section 104, and if the input bit stream corresponds to apredictive picture (P-picture) or a bi-directional picture (B-picture),motion-compensated blocks and the result of IDCT are combined and thenoutputted to the video display section 104.

In FIG. 1, the VLD section 102 and the video decoder are separated, butthe video decoder generally includes the VLD section 102 and the videodecoder 103.

In the present invention, the VLD section 102 and the video decoder 103are separately illustrated to obtain the snap image from the output ofthe VLD section 102.

Specifically, the DC extraction section 201 of the transcoder 105 a ofthe snap image processing section 105 in FIG. 2 receives the picturetype, color type, and DCT coefficients from the VLD section 102 in theunit of a macro block, and then extracts only the DC components from theDCT coefficients of the I-picture.

Also, the DC extraction section 201 discriminates whether the extractedDC component corresponds to the luminance (Y) or the color (C). If theextracted DC component corresponds to the luminance, the DC extractionsection 201 outputs the extracted DC component to the adder, while ifthe extracted DC component corresponds to the color, it outputs theextracted DC component directly to the DPCM section 203.

The adder obtains the average of the DC values with respect to fourmacro blocks of 8×8, and outputs the average value to the DPCM section203.

That is, as shown in FIG. 3, in the interlaced scanning sequence, thetop/bottom signal of the luminance has a different structure accordingto the DCT type (for example, frame DCT and field DCT).

However, the average value in the unit of a frame is obtained byaveraging four luminance blocks by the adder 202, and this results inthe constant values for each macro block.

In other words, by obtaining the DC values for four blocks, theinconsistency of the picture structure, i.e., the deviation of thetop/bottom position, can be solved.

Also, the compression rate can be reduced through the reduction of thestorage capacity and the estimation error produced during the DPCMoperation.

The DPCM section 203 obtains the difference value between the obtainedDC value and the DC value of the previous macro block for each Y/Csignal, and outputs the difference value to the Huffman encoding section204. The Huffman encoding section 204 heightens the compression rate byperforming the Huffman encoding.

Specifically, the DPCM section 203 obtains the difference between the DCcomponents of the present and previous macro blocks with respect to theY/C signal for each macro block. The Huffman encoding section 204applies the Huffman code to the difference value in a manner that asmall number of bits are allocated to a frequently appearing value, anda large number of bits are allocated to a rarely appearing value toreduce the whole number of bits. The Huffman-encoded values are storedin the storage device 106.

At this time, since the DC change among the macro blocks of the HD classimage is not great, a good compression rate can be obtained.

Also, the DPCM section 203 performs the DPCM in the unit of a slice.

Here, the slice is a line unit in the video snap image.

This is because in case of performing a one-dimensional DPCM, the DCvalue of the last macro block in a horizontal direction is quitedifferent from that of the first macro block in the horizontal directionin the next slice.

As described above, the DPCM section 203 performs the one-dimensionalDPCM by determining the pixels in the horizontal direction of a picturein the unit of a slice during encoding the DC image, and at this time,the first pixel has a pixel value from which 128 is subtracted.

Then, the difference between the present pixel value and the previouspixel value is Huffman-encoded.

FIG. 4 shows an example of the picture size of an interlaced scanningimage of 1920×1080 and the picture size of the snap image converted fromthe interlaced scanning image through the transcoder 105 a of the snapimage processing section 105.

The frame size after the transcoding is about 1/256 times smaller thanthe existing picture size.

This is because the purpose of the search device is to simply view thecontents of the image or to skip to a desired position rather than toview the image in detail.

At this time, in searching the stored image as shown in FIG. 1, the snapimage stored in the storage device 106 can be viewed through anon-screen display (OSD) or the video display section 104.

Also, the video snap image is displayed only as the intra-picture, andthus is used for the rapid search.

At this time, as shown in FIG. 5, the bit stream of the snap imagecompressed through the transcoder 105 a of FIG. 2 is packetized with thevideo ES, and then stored in the storage device 106.

FIG. 5 shows the database structure of the snap image and the video ESstored in the storage device 106 such as the HDD.

Referring to FIG. 5, when the video ES is to be reproduced in detail atthe position of the sequence searched through the snap image after thevideo ES and the snap image are stored in the storage device 106, thevideo ES and the snap image are multiplexed and stored in the storagedevice 106 so that the video ES can be directly reproduced through thevideo decoder without additional hardware.

That is, the video ES and the snap image do not exist as independentdatabases, but are combined together.

At this time, the snap images are distinctively stored without affectingthe existing MPEG syntax using the extension_start_code and theextension_start_code_identifier on the MPEG-2 syntax.

The bit stream of the snap image is composed of an image size,positional information of a slice 0 to slice N, data length, and videosnap data in the unit of a Huffman-encoded slice.

As described above, the bit stream of the snap image and the video ESare connected together to be stored as one signal train in the storagedevice 106, and this results in the following advantages.

First, if the reproduction is selected at a desired portion of the videosnap image, the video ES at the position can be directly reproduced.

Specifically, the snap image is composed of only the I-picture, and itsposition is just before the video ES. Thus, if the detailed reproductionis desired at the position when the snap image is displayed, the usermay select either of the direct reproduction or the video snap imagebeing displayed.

Since the original MPEG video bit stream indicates the intra picture,the following video ES is decoded by the VLD section 102 and the videodecoder 103, and then displayed on the display device.

That is, the reproduction is directly performed without the necessity ofsearching the desired display position.

Second, since the extension_start_code on the MPEG-2 syntax is used forthe discrimination of the snap image, the video ES stored in the storagedevice 106 can be directly inputted to the video decoder 103 without anyproblem.

That is, it is not required to separately remove the bit stream of thesnap image from the bit stream inputted to the video decoder 103.

For this, the snap image does not use theextension_start_code_identifier used in the video decoder 103.

The present invention proposes the use of one among theextension_start_code_identifiers B, C, D, E, and F remaining as spareson the MPEG syntax.

Thus, the video decoder 103 confirms the extension start_code_identifierin the input video ES, and if it is an unused signal on the MPEG syntax,for instance, if it is one among B, C, D, E, and F, the video decoder103 skips the signal without performing the decoding.

Meanwhile, the video ES to be stored in the storage device 106 is storedtogether with the PTS. This is because the PTS is required during thereproduction of the video ES.

That is, since the decoding order of the MPEG bit stream is differentfrom the displaying order thereof, the PTS is the signal required forthe decoding and displaying operation in the determined order.

Also, the PTS signal is very important to overflow or underflow of avideo buffer (not illustrated) in the video decoder 103.

Thus, by separately using a PTS_start_code, the PTS signal is storedalong with the video ES in the picture unit.

As a result, the PTS enables the video ES to be decoded to match withthe determined order without malfunction of the video buffer.

That is, the display time of the following decoded images is adjustedusing the PTS, and thus a stable buffer control can be obtained.

The present invention can be built in a TV receiver or a set top boxhaving a storage device such as an HDD.

Also, the present invention is an essential technique to the applicationfields such as a digital TV receiver or a digital video cassetterecorder (VCR) having a built-in storage device, and has a great effecton solidification of the technical competitiveness.

The present invention is also applicable to the implementation ofvarious kinds of video servers and private video recorders.

As described above, according to the apparatus for transcoding a videosnap image according to the present invention, only the video snap imageis preferentially decoded during the video search, and the contents of adesired video image can be searched more easily and rapidly.

Also, in a skip mode to the desired contents, if the snap image isselected when the desired snap image is displayed, the video image isdecoded and reproduced just from the position without additionalhardware.

Also, the stable control of the buffer can be obtained by adjusting thedisplay time of the following decoded images using the PTS.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An apparatus for transcoding a video snap image comprising: a videodecoder for performing a variable length decoding (VLD), inversediscrete cosine transform (IDCT), and inverse quantization with respectto an input video bit stream to display the decoded bit steam; a DCextraction section for extracting DC components from discrete cosinetransform (DCT) coefficients of variable-length-decoded macro blocks; anadder for averaging the extracted DC components; a differential pulsecode modulation (DPCM) section for obtaining and outputting a differencevalue between the DC component averaged by the adder or the DC componentoutputted from the DC extraction section and a DC component of aprevious macro block, wherein the DPCM section obtains the differencevalue between the DC component of a color extracted by the DC extractionsection and the DC component of a color of the previous macro block; aHuffman encoding section for Huffman-encoding the difference valueoutputted from the DPCM section; and a storage device for storing aHuffman-encoded snap image and the video bit stream as one signal train.2. The apparatus as claimed in claim 1, wherein if the extracted DCcomponents correspond to a luminance, the adder averages the extractedDC components of the luminance.
 3. An apparatus for transcoding a videosnap image comprising: a video decoder for performing a variable lengthdecoding (VLD), inverse discrete cosine transform (IDCT), and inversequantization with respect to an input video bit stream to display thedecoded bit stream; a DC extraction section for extracting DC componentsfrom discrete cosine transform (DCT) coefficients ofvariable-length-decoded macro blocks; an adder for averaging theextracted DC components; a differential pulse code modulation (DPCM)section for obtaining and outputting a difference value between the DCcomponent averaged by the adder or the DC component outputted from theDC extraction section and a DC component of a previous macro block,wherein the DPCM section obtains the difference value between the DCcomponent of a luminance averaged by the adder and the DC component of aluminance of the previous macro block; a Huffman encoding section forHuffman-encoding the difference value outputted from the DPCM section;and a storage device for storing a Huffman-encoded snap image and thevideo bit stream as one signal train.
 4. The apparatus as claimed inclaim 1, wherein the DCT coefficients used for extracting the DCcomponents through the DC extraction section comprise DCT coefficientsof an intra (I)-picture.
 5. The apparatus as claimed in claim 1, whereinthe DPCM section performs the DPCM in the unit of a slice.
 6. Anapparatus for transcoding a video snap image comprising: a video decoderfor performing a variable length decoding (VLD), inverse discrete cosinetransform (IDCT), and inverse quantization with respect to an inputvideo bit stream to display the decoded bit stream; a DC extractionsection for extracting DC components from discrete cosine transform(DCT) coefficients of variable-length-decoded macro blocks; an adder foraveraging the extracted DC components; a differential pulse codemodulation (DPCM) section for obtaining and outputting a differencevalue between the DC component averaged by the adder or the DC componentoutputted from the DC extraction section and a DC component of aprevious macro block; a Huffman encoding section for Huffman-encodingthe difference value outputted from the DPCM section; and a storagedevice for storing a Huffman-encoded snap image and the video bit streamas one signal train, wherein the video bit stream and the snap image bitstream to be stored in the storage device are connected together to bestored as the one signal train, and are discriminated from each otherusing an unused extension_start_code_identifier on an MPEG-2 syntax. 7.The apparatus as claimed in claim 6, wherein the bit stream of the snapimage to be stored in the storage device is composed of an image size,positional information of each slice, data length, and video snap datain the unit of a Huffman-encoded slice.
 8. The apparatus as claimed inclaim 6, wherein the video bit stream to be stored in the storage deviceis composed of a presentation time stamp (PTS) and a video elementarystream (ES) in the unit of a picture.
 9. The apparatus as claimed inclaim 6, wherein if a user selects the snap image being displayed, thevideo decoder decodes and displays the video bit stream stored in thenext position of the snap image being displayed.
 10. The apparatus asclaimed in claim 9, wherein the video decoder confirms theextension_start_code_identifier from the input video bit stream, andthen if the identifier is an identifier that is not used on the MPEGsyntax, the video decoder skips the video bit stream indicated by theidentifier without decoding the bit stream.
 11. A method of transcodinga video snap image comprising the steps of: variable-length-decoding aninput video bit stream in the unit of a macro block; extracting DCcomponents from discrete cosine transform (DCT) coefficients ofvariable-length-decoded macro blocks; obtaining a difference valuebetween the extracted DC component and a DC component of a previousmacro block, wherein obtaining the difference value between theextracted DC component and the DC component of the previous macro blockincludes if the extracted DC component corresponds to a luminance,averaging the extracted DC components of the luminance, and thenobtaining the difference value between the averaged DC component of theluminance and the DC component of the luminance of the previous macroblock; and Huffman-encoding the difference value.
 12. A method oftranscoding a video snap image comprising the steps of:variable-length-decoding an input video bit stream in the unit of amacro block; extracting DC components from discrete cosine transform(DCT) coefficients of variable-length-decoded macro blocks; obtaining adifference value between the extracted DC component and a DC componentof a previous macro block, wherein obtaining the difference valuebetween the extracted DC component and the DC component of the previousmacro block includes if the extracted DC component corresponds to acolor, obtaining the difference value between the extracted DC componentof the color and the DC component of the color of the previous macroblock; and Huffman-encoding the difference value.
 13. The method asclaimed in claim 11, wherein at the step of extracting the DCcomponents, the DCT coefficients from which the DC components areextracted are DCT coefficients of an intra (I)-picture.
 14. The methodas claimed in claim 11, wherein the step of obtaining the differencevalue is performed in the unit of a slice.
 15. The method as claimed inclaim 11, further comprising combining a Huffman-encoded snap image andinformation of the video bit stream.
 16. The method as claimed in claim15, wherein the Huffman-encoded snap image and the information of thevideo bit stream are combined as one signal train.
 17. The method asclaimed in claim 16, further comprising storing the one signal train ina storage device.
 18. The method as claimed in claim 11, wherein theinput video bit stream comprises an MPEG video stream.
 19. The apparatusas claimed in claim 1, wherein the input video bit stream comprises anMPEG video stream.
 20. An apparatus comprising: a video decoder toperform a variable length decoding, inverse discrete cosine transform,and inverse quantization of an input video bit stream; an extractionsection to extract DC components from discrete cosine transformcoefficients of variable-length-decoded macro blocks; an adder toaverage the extracted DC components, wherein the adder averages theextracted DC components of a luminance if the extracted DC componentscorrespond to the luminance; a differential pulse code modulationsection to output a difference value based on a DC component of aprevious macro block; an encoding section to encode the difference valueoutput from the differential pulse code modulation section; and astorage device to store a single bit stream including an encoded snapimage and information of the video bit stream.
 21. An apparatuscomprising: a video decoder to perform a variable length decoding,inverse discrete cosine transform, and inverse quantization of an inputvideo bit stream; an extraction section to extract DC components fromdiscrete cosine transform coefficients of variable-length-decoded macroblocks; an adder to average the extracted DC components; a differentialpulse code modulation section to output a difference value based on a DCcomponent of a previous macro block, wherein the differential pulse codemodulation section obtains the difference value between a DC componentof a luminance averaged by the adder and the DC component of a luminanceof the previous macro block; an encoding section to encode thedifference value output from the differential pulse code modulationsection; and a storage device to store a single bit stream including anencoded snap image and information of the video bit stream.
 22. Anapparatus comprising: a video decoder to perform a variable lengthdecoding, inverse discrete cosine transform, and inverse quantization ofan input video bit stream; an extraction section to extract DCcomponents from discrete cosine transform coefficients ofvariable-length-decoded macro blocks; an adder to average the extractedDC components; a differential pulse code modulation section to output adifference value based on a DC component of a previous macro block,wherein the differential pulse code modulation section obtains thedifference value between a DC component of a color extracted by the DCextraction section and the DC component of a color of the previous macroblock; an encoding section to encode the difference value output fromthe differential pulse code modulation section; and a storage device tostore a single bit stream including an encoded snap image andinformation of the video bit stream.
 23. An apparatus comprising: avideo decoder to perform a variable length decoding, inverse discretecosine transform, and inverse quantization of an input video bit stream;an extraction section to extract DC components from discrete cosinetransform coefficients of variable-length-decoded macro blocks; an adderto average the extracted DC components; a differential pulse codemodulation section to output a difference value based on a DC componentof a previous macro block; an encoding section to encode the differencevalue output from the differential pulse code modulation section; astorage device to store a single bit stream including an encoded snapimage and information of the video bit stream; and a device to connectthe video bit stream and the snap image bit stream to be stored in thestorage device as the single bit stream.
 24. The apparatus as claimed inclaim 23, wherein the bit stream of the snap image to be stored in thestorage device includes information of an image size, a positionalinformation of each slice, a data length, and video snap data in a unitof an encoded slice.
 25. The apparatus as claimed in claim 23, whereinthe video bit stream to be stored in the storage device includesinformation of a presentation time stamp (PTS) and a video elementarystream (ES) in a unit of a picture.
 26. The apparatus as claimed inclaim 20, wherein the input video bit stream comprises an MPEG videostream.